A preliminary investigation into the ultrastructure of dental calculus and associated bacteria

Though dental calculus is generally recognised as comprising mineralised bacteria, areas of non-mineralised bacteria may be present.

To investigate the ultrastructure of non-decalcified young and mature supragingival calculus and subgingival calculus, and the possible presence of internal viable bacteria.

Supragingival calculus was harvested from five patients, 9-10 weeks after scaling and root debridement. Five samples of mature supragingival and subgingival calculus were taken from patients presenting with adult periodontitis. Specimens were fixed and embedded for transmission electron microscopy.

The ultrastructure of young and mature supragingival calculus was similar with various large and small crystal types. Non-mineralised channels were observed extending into the calculus, often joining extensive lacunae, both containing intact non-mineralised coccoid and rod-shaped microorganisms. Subgingival calculus possessed more uniform mineralisation without non-mineralised channels and lacunae.

Supragingival calculus contains non-mineralised areas which contain bacteria and other debris. The viability of the bacteria, and their identification could not be determined in this preliminary investigation. As viable bacteria within these lacunae may provide a source of re-infection, further work needs to be done to identify the bacteria in the lacunae, and to determine their viability.